The present invention relates to self-heating cans or other containers holding beverages, food, medicine, epoxy resins and other materials that it is desired to heat before consuming or using. In particular, the present invention relates to an insertable themotic module for such self-heating containers.
Containers may have integral or separate insertable modules for warming materials in the container, such as Japanese sake, coffee, or soup. Examples of such self-heating containers with integral thermic modules are disclosed in U.S. Pat. Nos. 5,461,867 and 5,626,022, issued to Scudder et al and an example of a separately insertable module is disclosed in U.S. Pat. No. 6,134,894 to Searle, et al. Such containers typically include an outer can or body, in which the food or beverage is sealed and an elongated cavity or chamber which extends into the container body from the bottom end. The cavity is sized to accommodate the thermic module. The thermic module normally contains two chemical reactants which are stable when separated from one another, but when mixed in response to actuation of the thermic module by a user, produce an exothermic reaction (or, alternatively, an endothermic reaction) and thereby heat (or cool) the contents of the container. This elongated cavity functions as both a chamber in which to contain the reaction and a heat-exchanger for transferring heat between it and the surrounding contents of the container body. The thermic module usually has two chambers, each of which contains one of the chemical reactants, separated by a breakable barrier such as metal foil. Typically, one of the reactants is a liquid, and the other is in a powdered or granular solid form. Calcium oxide (quicklime) and water are examples of two reactants known to produce an exothermic reaction to heat the container contents. Other combinations of reactants (e.g. ammonium nitrate and water) produce endothermic reactions to cool the container contents. The thermic module cavity is normally sealed by an end-cap. The outside of the end-cap will serve as an actuator button that a user may depress to initiate the heating or cooling. The end-cap typically has a pushrod or similar prong-like member that extends from the actuator button nearly to the breakable barrier. Depressing the actuator button forces the prong into the barrier, puncturing it and thereby allowing the reactants to mix. The heat produced by the resulting exothermic reaction (or, alternatively, used by a resulting endothermic reaction) is transferred between the reaction chamber of the thermic module and the contents of the container body by conduction. The internal walls of the cavity may be fluted or pleated to promote such heat conduction. Exothermic reactions also typically generate a gas and/or steam, which is allowed to escape through vents in the end of the container. The user inverts the container and, when the contents have reached the desired temperature, consumes the contents. The end of the container body opposite the cavity has a seal or closure, such as conventional beverage container pull-tab or pop-top, that may be opened and through which the user may consume the heated or cooled contents.
One of the disadvantages associated with prior self-heating containers which place the chemical reactants directly into the cavity (i.e. an integral thermic module) is that the reactants typically cannot reliably be placed within the cavity before the container is filled with a food or beverage and subjected to the normal sterilization process. This is because the heat of the sterilization process may damage the reactants. It is generally not desirable to fill, sterilize, and pack the thermic modules into the containers at the same location. This is because the risk of contamination from the chemical reactants and because of the expense operating the module packing step in the same sterile environment required for filling and sealing the food or beverage in the containers. The current practice when employing integral thermic modules is to fill the container with the food or beverage and sterilize the container at one location, and then transport the containers to a second location for combining the container with the integral thermic modules. In some instances, it may even be necessary to return the containers to the original location for labeling, distribution or warehousing.
To be commercially acceptable, self-heating containers must be able to raise the temperature of the product to sufficiently high and in a sufficiently short period of time. An unofficial minimum standard accepted by many in the industry for heating type containers is that the thermic module must be able to raise the contents of the container at least 40° C. in less than 180 seconds.
While patents such as U.S. Pat. No. 6,134,894 to Searle, et al. have disclosed separately formed modules which insert into the cavity of the container, these prior art modules still possess many disadvantages. For example, it is desirable to have the walls of the cavity and those of the thermic module in contact to maximize heat transfer. However, it is often difficult to manufacture thermic module to the exact tolerance which allows the module to readily slide into the cavity and at the same time perfectly fit against the internal walls of the cavity. And while metals such as aluminum have good heat transfer characteristics, inevitably an air gap occurs between the module sidewalls and the internal walls of the cavity and acts as an insulating barrier. Prior art devices such as discussed in the Searle patent suggest using gels to fill air gaps, but gels have limited shelf-life because they tend to dry out.
It would be highly desirable to manufacture the modules from a material less expensive than metal, such as plastic. However, it has generally been accepted in the industry that the low thermal conductivity of plastics renders it totally impractical for a plastic thermic module to heat a container's contents to the desired 40° C. in less than 180 seconds. It is not believed that the prior art separately formed thermic modules are capable of reliably achieving this temperature/time requirement, particularly when dealing with standard sized soft drink cans. Therefore, a separately formed module capable of achieving this temperature/time standard would be an important and significant improvement in the art.
Another disadvantage existing in prior art devices is the process for manufacturing containers having a thermic module. This process includes three steps: 1) forming a cylindrical can body (such as by rolling and seaming a sheet of metal); 2) forming a separate bottom portion of the can which includes a thermic cavity and then attaching this bottom portion to the cylindrical body; and 3) crimping a lid onto the top of the cylindrical body. It would be a considerable improvement in the art if this process could be shortened to only two steps.